Theory of Pion-Nucleus Scattering Lengths

Abstract

The impulse or single-scattering approximation for zero-energy pion-nucleus scattering gives results in disagreement with the experimental scattering lengths obtained from pionic atoms. We calculate multiple-scattering corrections in a simple nuclear model, and show that double scattering of the pion can account for a major portion of the disagreement. The largest contributions involve incoherent excitation of the nucleus and are not included in most optical models. These contributions include the effect of nuclear binding on the scattering.